1. Field of the Invention
The present invention relates to L-lysine sulfate crystals and methods for making the crystals, and more specifically to diL-lysine sulfate crystals with crystal water incorporated into the structure, and a method of making these crystals in larger quantities which are readily separable from the mother liquor. Finally, the present invention relates to products containing L-lysine made by the above novel method.
2. Brief Description of the Related Art
L-lysine is one of the essential amino acids and is widely used in the pharmaceutical and agricultural industries as a nutrition regulator and feed additive, among other uses. It circulates primarily as L-lysine hydrochloride (www.ajinomoto.co.jp/ajinomoto/A-life/aminoscience/siryou/lijin.html). When in the form of diL-lysine sulfate, feed effects equivalent to those of L-lysine hydrochloride are seen (Roth et al., 1994: Biological Efficiency of L-Lysine Base and L-Lysine Sulphate Compared with L-Lysine HCl in Piglets; Agribio. Res. 47(2):177–186 (1994)).
Crystals of diL-lysine sulfate are known to contain anhydrous diL-lysine sulfate (Aketa et al., Stereo chemical studies XL A biomimetic conversion of L-lysine into optically active 2-substituted; Chem. Pharm. Bull. 24(4):623–31 (1976)). Therefore, alcohol is often added to the diL-lysine sulfate aqueous solution to enable production of anhydrous diL-lysine sulfate crystals. Because the added alcohol must be removed from the resulting crystals, an extra purification step must be added to the process, further reducing the yield of crystals. See Aketa et al.
Anhydrous diL-lysine sulfate crystals are known to be highly soluble in water, which also contributes to the low yields of crystals. As a result, the high concentration of crystals in the mother liquor causes a decreased rate of crystallization. The small amounts of crystals that are eventually obtained are very fine and small, which causes a difficult separation from the mother liquor, further exacerbating the low yield problem.
Therefore, there is clearly a need in the art for improved methods of obtaining pure and highly separable L-lysine crystals. As L-lysine is such an important component in products for many different industries, highly efficient methods for crystallizing and purifying L-lysine are clearly needed in the art.
The present invention describes a novel method for crystallization and purification of L-lysine that is highly efficient, provides significantly increased yields, and results in easier and more efficient separation of the product crystals from the mother liquor. The present invention also describes a novel crystal form of L-lysine sulfate.